[MCParser] Set default alignment value when meeting invalid align

[serge-sans-paille]

Summary

Upon invalid alignment value, still set a default valid alignment value to avoid
hitting later asserts.

Fix #55273

[nikic]

Is it possible to add a test for this?

[serge-sans-paille]

In D125688#3515834, @nikic wrote:

Is it possible to add a test for this?

I wonder... is there a way to make the difference between an error and an abort? Because without this patch we get an error message followed by an abort, and with this patch we only get the error.

[nikic]

In D125688#3515930, @serge-sans-paille wrote:

In D125688#3515834, @nikic wrote:

Is it possible to add a test for this?

I wonder... is there a way to make the difference between an error and an abort? Because without this patch we get an error message followed by an abort, and with this patch we only get the error.

I think a test that aborts would always fail by default unless not --crash is used.

[serge-sans-paille]

+ test case

[serge-sans-paille]

Fix test case

[serge-sans-paille]

Update existing test case

[serge-sans-paille]

Gentle ping :-) I'm a little unsure on the value change upon error, but that's also a bit strange to issue an error but still generate some output.

[nikic]

llvm/lib/MC/MCParser/AsmParser.cpp

3457

What if the alignment is a non-pow2 greater than 32-bit? I think that case will sneak through.

[serge-sans-paille]

Address reviewer comment and add an extra test case to capture the issue.

[nikic]

LGTM

llvm/lib/MC/MCParser/AsmParser.cpp

if (IsPow2) {
 
     Alignment = 1ULL << Alignment;
   } else {
     // Reject alignments that aren't either a power of two or zero,
     // for gas compatibility. Alignment of zero is silently rounded
     // up to one.
     if (Alignment == 0)
       Alignment = 1;
-    if (!isPowerOf2_64(Alignment))
+    else if (!isPowerOf2_64(Alignment)) {
       ReturnVal |= Error(AlignmentLoc, "alignment must be a power of 2");
-    if (!isUInt<32>(Alignment))
+      Alignment = PowerOf2Floor(Alignment);
+    }
+    if (!isUInt<32>(Alignment)) {
       ReturnVal |= Error(AlignmentLoc, "alignment must be smaller than 2**32");
+      Alignment = 1u << 31;
+    }
   }
 
   // Diagnose non-sensical max bytes to align.
   if (MaxBytesLoc.isValid()) {
     if (MaxBytesToFill < 1) {
       ReturnVal |= Error(MaxBytesLoc,
                          "alignment directive can never be satisfied in this "
                          "many bytes, ignoring maximum bytes expression");

llvm/test/MC/AsmParser/directive_align.s

 # RUN: not llvm-mc -triple i386-apple-darwin9 %s 2> %t.err | FileCheck %s
 # RUN: FileCheck < %t.err %s --check-prefix=CHECK-WARN
 
 # CHECK: TEST0:
 # CHECK: .p2align 1
 TEST0:  
         .align 1
 
 # CHECK: TEST1:
 # CHECK: .p2alignl 3, 0x0, 2
 TEST1:  
         .align32 3,,2
 
 # CHECK: TEST2:
-# CHECK: .balign 3, 10
+# CHECK-WARN: error: alignment must be a power of 2
+# CHECK: .p2align 1, 0xa
 TEST2:  
         .balign 3,10
 
 # CHECK-WARN: p2align directive with no operand(s) is ignored
 TEST3:  
         .p2align
+
+# CHECK: TEST4:
+# CHECK: .p2align  31, 0x90
+# CHECK-WARN: error: alignment must be smaller than 2**32
+TEST4:  
+        .balign 0x100000000, 0x90
+
+# CHECK: TEST5:
+# CHECK: .p2align  31, 0x90
+# CHECK-WARN: error: alignment must be a power of 2
+# CHECK-WARN: error: alignment must be smaller than 2**32
+TEST5:  
+        .balign 0x100000001, 0x90
+